In many modern digital wireless communications systems, such as CDMA2000 (a third generation code-division multiple access (CDMA) based wireless communications system), one or more control channels are used to send control information from a base station (BS) to a mobile station (MS). The information on the control channel(s) may be used to provide information related to data channels, wake-up from a control hold mode, and so forth.
In a CDMA2000 wireless communications system, up to two Forward-Link Packet Data Control Channels (FPDCCH) may be used to send control information to a MS in order to decode a Forward-Link Packet Data Channel (FPDCH) amongst other things. The two FPDCCH channels are code-division multiplexed and is associated with one of two FPDCHs. A single FPDCH is also time-division multiplexed and serves packet data to users. At any given time, each FPDCH can be allocated to one user. The duration of time of a single allocation can be 1, 2, or 4 time slots, with each time slot being 1.25 milliseconds (ms) in duration. The length of a single allocation may be dependent upon many factors, including channel conditions, amount of contention, and so on.
The two FPDCCH channels and the two FPDCH channels match one another in slot format and duration. In other words, if the first FPDCCH is allocated to a user for one time slot, then the second FPDCCH and the two FPDCH channels are also allocated for one time slot. When a number of time slots have been allocated to a particular user, the FPDCH is then populated with user data and the assigned FPDCCH is populated with control information.
A MS needs to continually monitor the FPDCCH in order to ensure that it receives information intended for it. To do so, the MS usually needs to decode both of the FPDCCH channels, read the contents, and determine if data on the associated FPDCH is intended for it. If the MS ID on the FPDCCH matches its own, then the MS attempts to decode the FPDCH.
A straightforward implementation that is commonly used to decode the FPDCCH is to have the MS decode each time slot as if the time slot were part of a one slot, two slot, and four slot allocation format. This decoding is required since the MS has no prior knowledge of the particular format that is being transmitted on the FPDCCH. This implies that, for example, in a four slot allocation example, by the time the MS decodes a fourth time slot and knows for sure that the MS ID of the intended recipient of the FPDCCH and the FPDCH, it had to have decoded the four time slots a total of 12 times (4 time slots*3 decode operations per time slot).
One disadvantage of the prior art is due to the requirement that each time slot be tested for each of the three possible formats, a significant amount of processing power and overhead is expended. For each time slot, two out of the three tests will be shown to be false. Therefore, it takes mobile stations additional processing power in order to perform the testing and at the same time, perform other needed operations. The additional processing power may result in a greater overall cost for the mobile station due to the need for a processing unit with greater capabilities.
A second disadvantage of the prior art is that the additional testing results in the consumption of additional battery power, thereby shortening battery life of a mobile station or requiring a larger battery with greater capacity. This may involve the addition of more weight or the use of more advanced (more expensive) battery technology.